This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on patent application No(s). 92124251 filed in Taiwan on Sep. 2, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus for reducing warm-up time of a lamp and the method for the same, and particularly to a method for reducing start-up time of a scanner by auxiliary light source.
2. Description of the Related Art
In general operation of a scanner, a light source is needed to illuminate the documents to be scanned in order that the scanned image data of the document can be obtained by an optical image sensor module, such as a CCD module, in the scanner.
In light of the above, the scan quality of the scanner is based on the light source, and therefore scanner manufacturers have paid much attention to researches and developments in the light source of scanners.
In addition, because scanners need the higher luminance, cold cathode fluorescent lamps (CCFLs) are adopted by mostly scanner manufacturers.
In consideration of the illumination quality, when the cold cathode fluorescent lamp is used as a light source, the scanner is designed to start a scan operation only when the cold cathode fluorescent lamp reaches a certain temperature, so the light emitted from the cold cathode fluorescent lamp is stable for scanning. Accordingly, upon turning on a scanner, it usually takes a warm-up time for a cold cathode fluorescent lamp to reach a sufficient temperature for stable illumination. Please refer to FIG. 1, which shows a curve representing the warm-up time to luminance characteristic of a typical cold cathode fluorescent lamp.
At the present time, the typical warm-up time of a cold cathode fluorescent lamp is approximately 90 seconds, which the users are not satisfied with, and hence scanner manufacturers tend to develop techniques for reducing the warm-up time to eliminate the dissatisfaction.
Therefore, a method for rapid warm-up of a cold cathode fluorescent lamp, such as the dual input voltage control scheme disclosed in U.S. Pat. No. 5,907,742, has been developed. That is, higher input voltage level (approximately 12 volts) is used during warm-up period to rapidly heat the cold cathode fluorescent lamp and hence to reach the operating temperature in early time, while lower input voltage level (approximately 8 volts) is used after the warm-up of the lamp. The above control scheme significantly reduces the warm-up time of the cold cathode fluorescent lamp to approximately 30 seconds. However, in order for fast warm-up of the lamp in the method, the cold cathode fluorescent lamp bears a higher current during warm-up period, which results in degradation of the lamp operational life.
Moreover, in order to create two different voltage levels respectively for warm-up period and for operational period, a pulse width modulator circuit which is a complicated circuit design, is provided to control the input voltage.
In addition, the frequency oscillator utilized in the above patent and built-in in the inverter, has an oscillation frequency drifting between 35˜45 KHz under different voltages and temperatures. This will consequently cause unstable illumination and hence degrade the scan quality.
An alternative method for fast warm-up of a cold cathode fluorescent lamp is to provide a heating wire to the periphery of the lamp. In this case, the heating wire is wound around the outer surface of the cold cathode fluorescent lamp, and, with the aid of heat generated by the heating wire around the lamp, the lamp temperature may be forced to increase more rapidly to thus achieve the fast warm-up. Although the fast warm-up of the lamp can be well-achieved by this method, an additional component, i.e., the heating wire, is required to be provided to the periphery of the lamp and thus some additional steps must be added to the production process.
Furthermore, providing a heating wire adds up to increased costs, including the component cost and the power consumption cost. The most serious problem is that the heating wire wound around the outer surface of the lamp partially blocks the light emitted from the lamp, which causes uneven illumination distribution of the cold cathode fluorescent lamp and in turn degrade the scan quality.
In view of the above, for rapid warm-up of cold cathode fluorescent lamps, those methods currently used in the art are very limited and still have unsolved problems. Therefore, the inventor has employed technical ideas and developed an innovative invention different from the above-mentioned conventional methods.